Micromachined cutting blade formed from {211}-oriented silicon

ABSTRACT

A cutting blade is disclosed fabricated of micromachined silicon. The cutting blade utilizes a monocrystalline silicon substrate having a {211} crystalline orientation to form one or more cutting edges that are defined by the intersection of {211} crystalline planes of silicon with {111} crystalline planes of silicon. This results in a cutting blade which has a shallow cutting-edge angle θ of 19.5°. The micromachined cutting blade can be formed using an anisotropic wet etching process which substantially terminates etching upon reaching the {111} crystalline planes of silicon. This allows multiple blades to be batch fabricated on a common substrate and separated for packaging and use. The micromachined cutting blade, which can be mounted to a handle in tension and optionally coated for increased wear resistance and biocompatibility, has multiple applications including eye surgery (LASIK procedure).

GOVERNMENT RIGHTS

[0001] This invention was made with Government support under ContractNo. DE-AC04-94AL85000 awarded by the U.S. Department of Energy. TheGovernment has certain rights in the invention.

FIELD OF THE INVENTION

[0002] The present invention relates in general to cutting instruments,and in particular to a micromachined cutting blade formed ofmonocrystalline silicon having a {211} crystalline orientation, and to amethod for manufacture thereof.

BACKGROUND OF THE INVENTION

[0003] Laser in-situ keratomelleusis (LASIK) is a procedure that iswidely used for laser eye surgery to correct refractive errors producingnearsightedness, farsightedness or astigmatism. The use of the LASIKprocedure requires a mechanical keratome to cut a thin circular flapacross the cornea of a patient's eye so that an eximer laser can then beused to remove a calibrated amount of underlying tissue from the corneato achieve a desired refractive change. The mechanical keratome aspresently used comprises a stainless steel knife blade which is rapidlyoscillated during use.

[0004] Metal cutting blades can have ragged or uneven cutting edges, andcan form burrs extending outward from the cutting edge. Metal cuttingblades can also dull during surgical use. These defects, if present onthe blade's metal cutting edge, can produce incisions that are raggedand uneven and that extend beyond a desired or critical depth. This canbe harmful in reducing the precision of the surgical procedure, inincreasing the time required for healing after surgery, and in affectingthe patient's vision correction as a result of the surgery. To limitthese harmful effects, a careful microscopic inspection of the blade'scutting edge during manufacture and before use must be performed whichincreases the cost of the blades and results in some blades beingrejected as unsuitable for surgery. What is needed is a knife blade forkeratomy that has a high degree of sharpness, and which can be reliablyproduced at low cost. Also needed is a knife blade which maintains itssharpness during use, and is not subject to the formation of burrs.

[0005] The present invention provides a solution to this problem byproviding a cutting blade (i.e. a knife blade) formed of monocrystallinesilicon that can be precisely sharpened by anisotropic etching andwhich, in the absence of any applied coatings, is incapable ofdeveloping burrs because of its crystalline nature.

[0006] The use of monocrystalline silicon with a {100} substrateorientation for forming a knife blade is disclosed in U.S. Pat. No.5,579,583 to Mehregany et al. Mehrenany's requirement for a{100}-oriented substrate produces a blade having a cutting angledetermined by the intersection of two crystalline planes, with thecutting angle being crystallography fixed at a relatively large bladeangle of either 54.7° or 109.4°. These relatively large blade angles aredisadvantageous for use in eye surgery since the large blade angleswould effectively reduce the sharpness of the blade and would also makeit difficult for the delicate cornea flap to easily slide across theblade during cutting.

[0007] The use of monocrystalline silicon for forming various types ofknife blades is also disclosed in U.S. Pat. Nos. 5,842,387 to Marcus etal; 5,928,161 to Krulevitch et al; and 5,980,518 to Carr et al. None ofthese references disclose the use of a {211} substrate orientation forforming a knife blade as used according to the present invention.Additionally, none of these references disclose a cutting edge formed inmonocrystalline silicon by a pair of substantially planar cutting-edgesurfaces aligned along crystalline planes of silicon and intersecting atan angle of less than 30 degrees.

[0008] An advantage of the present invention is that a cutting blade canbe fabricated that is substantially free from any burrs or raggedcutting edges.

[0009] Another advantage of the present invention is that a cuttingblade can be formed with a shallow cutting-edge angle of less than 30degrees, and preferably less than 20 degrees.

[0010] A further advantage of the present invention is that the cuttingedge of the blade can be coated with a deposited material such assilicon nitride, titanium nitride, tungsten, amorphous diamond orparylene for improved wear resistance, reduced friction orbiocompatibility.

[0011] Yet another advantage of the present invention is that aplurality of cutting blades can be formed on a single silicon substrate(i.e. a wafer) in a batch fabrication process and then be individuallyseparated.

[0012] Still another advantage of the present invention is thatsingle-edged and double-edged cutting blades can be formed according tothe present invention.

[0013] These and other advantages of the method of the present inventionwill become evident to those skilled in the art.

SUMMARY OF THE INVENTION

[0014] The present invention relates to a micromachined cutting bladethat comprises an elongate body of monocrystalline silicon having a pairof substantially parallel major body surfaces, with each major bodysurface being aligned substantially coplanar with a {211} crystallineplane of silicon, and a substantially planar cutting edge formed in themonocrystalline silicon body at an angle to one of the major bodysurfaces and oriented along the length of the body. The cutting-edgeangle is preferably 19.5 degrees and corresponds to the intersection ofa {211} crystalline plane of silicon with a {111} crystalline plane ofsilicon. The cutting edge is formed by anisotropically etching themonocrystalline silicon body, with the etching terminating at a {111}crystalline plane of silicon. In some embodiments of the presentinvention, the cutting edge of the blade can be hardened for increasedwear resistance by forming a coating of a hard material over at least apart of the cutting edge. The coating can comprise silicon nitride,titanium nitride, tungsten, or amorphous diamond. Alternately, aconformal parylene coating can be formed over a portion or: the entiretyof the cutting blade. The cutting blade can also include a handleconnected to opposite ends of the crystalline silicon body to supportthe body in tension, thereby keeping the cutting edge planar. Such ahandle can be, for example, U-shaped.

[0015] The present invention further relates to a micromachined cuttingblade that comprises an elongate body of monocrystalline silicon havinga pair of substantially parallel major body surfaces, and at least onecutting edge formed in the monocrystalline silicon body, with eachcutting edge further comprising a pair of cutting-edge surfaces alignedalong crystalline planes of silicon and intersecting at an angle ofgenerally less than 30 degrees, and preferably less than 20 degrees. Oneof the surfaces of each cutting edge is aligned substantially coplanarwith one of the body surfaces which, in turn, is substantially coplanarwith a {211} crystalline plane of silicon. The other surface of eachcutting edge is aligned substantially along a {111} crystalline plane ofsilicon. A coating of a hard material (e.g. silicon nitride, titaniumnitride, tungsten, or amorphous diamond) can be provided to cover atleast a part of one cutting edge of the blade to increase its wearresistance. Alternately, a conformal parylene coating can be formed overat least a portion of the cutting blade.

[0016] The present invention also relates to a method for forming amicromachined cutting blade, comprising steps for providing amonocrystalline silicon body having a pair of substantially parallelmajor body surfaces, with each major body surface being alignedsubstantially along a {211} crystalline plane of silicon; and forming atleast one cutting edge in the monocrystalline silicon body by forming anetch mask over each body surface, with the etch mask formed over atleast one of the body surfaces having an elongate opening therethroughto expose a portion of the body surface wherein the cutting edge is tobe formed; anisotropic etching the exposed portion of the body surfacethrough the opening in the etch mask down to the opposite body surface;and removing each etch mask. Each cutting edge is aligned substantiallyalong a {111} crystalline plane of silicon. This can be done by using ananisotropic wet etchant such as potassium hydroxide (KOH), tetramethylammonium hydroxide (TMAH) or ethylenediamine pyrocatechol (EDP).

[0017] Each cutting edge can also be hardened by depositing a coating ofa hard material (e.g. silicon nitride, titanium nitride, tungsten oramorphous diamond) over at least a part of the cutting edge. Thiscoating can be deposited by a conventional vapor deposition process.Alternatively, a conformal coating of parylene can be deposited over atleast a portion of each cutting blade.

[0018] Finally, a handle can be attached to the monocrystalline siliconbody to hold the monocrystalline silicon body and each cutting edge intension. Such a handle can be, for example, U-shaped.

[0019] Additional advantages and novel features of the invention willbecome apparent to those skilled in the art upon examination of thefollowing detailed description thereof when considered in conjunctionwith the accompanying drawings. The advantages of the invention can berealized and attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated into and form apart of the specification, illustrate several aspects of the presentinvention and, together with the description, serve to explain theprinciples of the invention. The drawings are only for the purpose ofillustrating preferred embodiments of the invention and are not to beconstrued as limiting the invention. In the drawings:

[0021]FIG. 1A shows a schematic perspective view of a micromachinedcutting blade formed according to the present invention and mounted on aU-shaped handle.

[0022]FIG. 1B shows a schematic cross-section view of the micromachinedcutting blade along the section line 1-1 in FIG. 1A.

[0023] FIGS. 2A-2E show a series of processing steps for forming a firstexample of the present invention in the form of a single-edged cuttingblade.

[0024] FIGS. 3A-3E show a series of processing steps for forming asecond example of the present invention in the form of a double-edgedcutting blade.

DETAILED DESCRIPTION OF THE INVENTION

[0025] Referring to FIG. 1A, there is shown schematically a firstexample of a micromachined cutting blade 10 formed according to thepresent invention, with the blade 10 being mounted in tension on aU-shaped handle 26. This example of the cutting blade 10 is single-edgedand comprises an elongate body 12 (also termed herein a substrate) ofmonocrystalline silicon having a pair of substantially parallel majorbody surfaces 14 and 14′ and a substantially planar cutting edge 16formed at an acute angle θ to one of the major body surfaces (i.e.surface 14′ in FIG. 1A) and oriented along the length of the body 12.The angle θ is generally less than 30° and preferably less than 20°.

[0026] In FIG. 1A, the monocrystalline silicon body 12, which can bepart of a lightly-doped (e.g. ≦5×10¹⁹ cm⁻³) monocrystalline siliconsubstrate (also referred to as a wafer), has major body surfaces 14 and14′ oriented substantially coplanar with a {211} crystalline plane ofsilicon (i.e. the surfaces 14 and 14′ are formed substantially parallelto the {211} crystalline plane during fabrication of the substrate 12wherefrom the cutting blade 10 is formed). This orientation isadvantageous for producing a shallow angle θ for the cutting edge 16using anisotropic wet etching as will be described in detailhereinafter. The shallow-angle cutting edge 16 is shown in detail in across-section view of the cutting blade 10 in FIG. 1B.

[0027] Fabrication of the single-edged cutting blade 10 in the exampleof FIGS. 1A and 1B will now be described with reference to FIGS. 2A-2Ewhich describe a series of silicon micromachining process steps. Thoseskilled in the art will understand that generally rectangular cuttingblades 10 of arbitrary dimensions can be fabricated using the siliconmicromachining process described hereinafter. Furthermore, althoughfabrication of a single cutting blade 10 will be described, thoseskilled in the art will understand that the teachings of the presentinvention can be used to batch fabricate a plurality of cutting blades10 of the same or different sizes on a common silicon substrate having adiameter of, for example, 4-8 inches. The individual blades 10 can thenbe separated either as a result of the anisotropic etching process (e.g.by anisotropically etching a plurality of sides of the blade 10 duringformation of the cutting edge 16), or by sawing, cleaving, laser cuttingetc. of one or more unetched sides of the blades 10. It should be notedthat anisotropic etching of the two sides of the blade 10 adjacent tothe cutting edge 16 results in the etching process being terminated uponreaching {111} crystalline planes of silicon that are oriented at anangle φ=61.9° degrees as measured from the major body surface 14′ (seeFIG. 1A). Furthermore, anisotropic etching of a side of the blade 10opposite the cutting edge 16 results in the etching process beingterminated at a {111} crystalline plane that is oriented 90° withrespect the major body surfaces 14 and 14′ (see FIG. 2B wherein thistype of {111} plane is labelled “22”).

[0028] In FIG. 2A, a {211}-oriented monocrystalline silicon substrate 12is provided for use in forming the cutting blade 10. The major bodysurfaces 14 and 14′ of the substrate 12 are blanketed with an etch mask18, with the etch mask 18 having an elongate (e.g. rectangular orU-shaped) opening 20 therethrough at a location wherein the cutting edge16 is to be formed. The etch mask 18 can comprise, for example, about500 nanometers of a silicate glass deposited by chemical vapordeposition (CVD) from the decomposition of tetraethylortho silicate(also termed herein as TEOS) and densified by heating to a hightemperature for a specified period of time. The exact thickness of theetch mask 18 will depend upon the thickness of the substrate 12 beingetched, and upon the particular anisotropic wet etchant being used.

[0029] After blanketing both surfaces 14 and 14′ of the substrate 12with the etch mask 18, the opening 20 in FIG. 2A can be formed byspinning a layer of photoresist (not shown) over the etch mask 18 on atop side of the substrate 12 and photolithographically defining aphotoresist mask having a shaped opening identical to that of theopening 20 to be formed through the etch mask 18. Reactive ion etchingcan then be used to locally, remove the TEOS glass to form the opening20 as shown in FIG. 2A with the patterned photoresist layer protectingthe remainder of the TEOS glass from being etched. After formation ofthe opening 20, the photoresist layer can be removed, leaving thepatterned etch mask 18 in place. If needed, this process can be repeatedto form a second opening 20 in the etch mask 18 covering the major bodysurface 14′ (e.g. to form a double-edged cutting blade 10 as shown inFIGS. 3A-3E).

[0030] In FIG. 2B, the patterned etch mask 18 is used to selectivelyremove the underlying silicon material from the substrate 12 using ananisotropic wet etchant such as potassium hydroxide (KOH), tetramethylammonium hydroxide (TMAH) or ethylenediamine pyrocatechol (EDP). The anisotropic wet etchant selectively etches away the silicon substratematerial over time without substantially attacking the etch mask 18. Theanisotropic nature of the etching process results in the etching slowingdown considerably upon reaching {111} crystalline planes of silicon sothat the etching can be considered as being substantially terminatedupon reaching the {111} planes. Meanwhile, the etching continues inother directions until other {111} crystalline planes are reached. As aresult, after being etched for up to a few hours the substrate assumesthe shape shown in FIG. 2B with a first {111} crystalline plane formingthe substantially planar cutting edge 16 oriented at the angle θ=19.5°with respect to the major body surface 14′, and with a second {111}crystalline plane 22 being oriented at an angle of 90° with respect tothe same surface 14′. The opening 20 in the etch mask 18 is preferablymade sufficiently wide so that the anisotropic etching extendscompletely through the thickness of the substrate to delineate a firstsubstrate portion 12 which is used to form the cutting blade 10, and asecond substrate portion 12′ which can later be discarded oncefabrication of the cutting blade 10 is completed.

[0031] In FIG. 2C, the etch mask 18 is removed (i.e. stripped) from thesubstrate leaving the substrate portions 12 and 12′ which are connectedtogether at locations outside the elongate opening 20. Stripping of theetch mask 18 can be performed, for example, by etching with a selectivewet etchant comprising hydrofluoric acid (HF). The HF-based etchantselectively etches the TEOS or other silicate glass forming the etchmask 18 while not substantially attacking silicon.

[0032] In FIG. 2D, the cutting blade 10 can be separated from thesubstrate portion 12′ and any remaining substrate material using aconventional dicing technique such as saw cutting, laser cutting, orcleaving. In some instances, all sides of the blade 10 can beanisotropically etched so that the etching process separates the blade10 from any remaining substrate material. The blade 10 can then bemounted onto an appropriate handle 26 for use.

[0033] For use in the LASIK procedure as described previously, thecutting blade 10 can be formed with a length that is generally in therange of 5-20 millimeters, a width of generally 1-5 millimeters, and asubstrate thickness of generally 0.05-1 millimeter. For otherapplications, the cutting blade 10 can be formed with different lateraldimensions and thickness. For use in the LASIK procedure, the cuttingblade 10 is preferably held in tension at its ends so that the blade canbe used to make substantially planar cuts when the blade is reciprocatedback and forth along its major axis and/or urged forward in a directionperpendicular to the major axis.

[0034] To hold the cutting blade 10 in tension, a generally U-shapedhandle 26 can be used as shown in FIG. 1A, with the blade 10 beingattached to the handle 26 at both ends under tension. The form ofattachment, which will depend upon a particular design and material forthe handle 26, can be, for example, solder 28 as shown in FIG. 1A, oralternately an adhesive (e.g. epoxy), screws or a pair of mechanicalclamps at each end of the handle 26.

[0035] The blade 10 can be mounted on the handle 26 under tension, forexample, by heating the blade 10 and the handle 26 when soldering theblade 10 the handle 26. By selecting the material (e.g. a metal or metalalloy, glass or fused silica) for the handle 26 to have a differentcoefficient of thermal expansion than that of the silicon blade 10, theblade 10 can be drawn into tension upon cooling of the handle 26 andblade 10 down to room temperature after the blade 10 is soldered to thehandle 26.

[0036] As another example, when the blade 10 is attached to the handle26 using an adhesive, screws or mechanical clamps, the handle 26 can belaterally compressed (e.g. in a vise) to reduce its length during thetime when the blade 10 is being attached to the handle 26. Once theattachment is complete, the handle 26 can be restored to its formercondition (e.g. by being removed from the vise) whereupon its length isincreased to draw the blade 10 into a state of tension. Those skilled inthe art will understand that other methods are available to attach thecutting blade 10 permanently or detachably to the handle 26.Furthermore, those skilled in the art will understand that other shapescan be provided for the handle 26, depending upon particular uses forthe cutting blade 10.

[0037] To aid in aligning the blade 10 to the handle 26 and/or toproperly tension the blade 10, optional alignment holes (not shown) canbe-etched or drilled through the blade 10 at either end for mating topins (not shown) protruding from the ends of the handle 26.

[0038] In FIG. 2E an optional coating 24 can be formed over the cuttingedge 16 and/or one or more edge-adjoining surfaces (i.e. the major bodysurfaces 14 and 14′). The coating 24 can be formed at the stage ofcompletion of the blade 10 shown in FIG. 2C (i.e. after removal of theetch mask 18 but while the blade 10 is still attached to substrateportion 12′ along with other blades 10 formed on the same substrate).Alternately, the coating 24 can be formed on the cutting blade 10 afterremoval of the substrate portion 12′ as shown in FIG. 2D. The coating 24can either comprise a hard material for improving the strength anddurability of the cutting edge 16 and edge-adjoining surfaces 14 and14′, or can comprise a conformal coating of parylene to reduce frictionand improve biocompatibility of the cutting blade 10. Here, it should benoted that silicon is a biocompatible material so that no additionalcoating need be applied for surgical use.

[0039] The hard material can be, for example, silicon nitride, titaniumnitride, or amorphous diamond deposited by a CVD process. Alternately,the hard material can be tungsten formed by a chemical reaction of atungsten-containing gas such as tungsten hexafluoride (WF₆) with thesilicon substrate material.

[0040] CVD deposition of silicon nitride and titanium nitride coatingsare widely used in the semiconductor industry and are well-known tothose skilled in the art so that they need not be described in greatdetail herein. Such silicon nitride or titanium nitride coatings 24 canbe deposited by conventional low-pressure chemical vapor deposition(LPCVD) to a layer thickness of, for example, 0.1 to 10 μm. A low-stresssilicon nitride coating 24 can be deposited, for example, by LPCVD at atemperature of 850° C. The deposition of titanium nitride can take placeby LPCVD at about the same temperature.

[0041] Amorphous diamond can also be used to provide a hard coating 24over the cutting edge 16 and/or the edge-adjoining surfaces 14 and 14′.Many different types of amorphous diamond coatings are known in the art,with each type of amorphous diamond comprising carbon atoms in aparticular bonding arrangement. One type of amorphous diamond that isparticularly well-suited for use forming the hard coating 24 is alow-stress amorphous tetrahedrally-coordinated carbon form (also termedherein as “a-tC”) which contains a high percentage (generally ≧70%) ofdiamond-like bonds (i.e. 4-fold coordinated carbon atoms with sp¹ hybridbonding), and with the remainder of the bonds therein beinggraphite-like bonds (i.e. 3-fold coordinated carbon atoms with sp²hybrid bonding). This a-tC coating 24 is transparent, insulating,smooth, extremely hard and contains negligible amounts (<0.1%) ofhydrogen.

[0042] The a-tC coating 24 can be formed on the cutting edge 16 oredge-adjoining surfaces 14 and 14′ by using pulsed laser deposition(PLD) with a rotating graphite target at room temperature which isirradiated by a krypton fluoride (KrF) laser operating at a wavelengthof 248 nanometers and at a high laser fluence of ≧50 Joules-cm⁻². Priorto deposition, the cutting blade 10 can be immersed briefly into adilute HF solution for up to a few minutes to provide a clean surfaceupon which the a-tC coating 24 can be deposited. The a-tC coating 24 canthen be deposited using PLD to a coating thickness of, for example,150-200 nanometers.

[0043] After deposition, the a-tC coating 24 is thermally annealed toreduce the stress therein as a result of the deposition process. Thisannealing step does not substantially affect the diamond-like propertiesof the a-tC coating 24, including its hardness. The annealing step canbe performed, for example, by using a rapid thermal annealer (RTA) toquickly bring the cutting blade 10 with the deposited a-tC coating 24 upto an annealing temperature of about 600° C. in an inert gas (e.g.argon) ambient, with the cutting blade 10 being held at this temperaturefor a time period from a few minutes up to about one hour. Thea-tC-coated cutting blade 10 can then be rapidly cooled back to roomtemperature after annealing. Thicker a-tC coatings 24 (e.g. up to 1-3 μmthick) can be formed by using a series of repeated deposition andannealing steps as described above to build the coating 24 up to apredetermined layer thickness. Further details of the a-tC coatingprocess are disclosed in an article by J. P. Sullivan et al, “StressRelaxation and Thermal Evolution of Film Properties in AmorphousCarbon,” Journal of Electronic Materials, vol. 26, pp. 1021-1029, 1997,which is incorporated herein by reference.

[0044] The formation of a tungsten coating 24 over the monocrystallinesilicon cutting blade 10 can be performed as described hereinafter. Theblade 10 is initially cleaned to remove any organic material. This canbe done by exposing the silicon surfaces to an oxidizing ambient (e.g.an oxygen plasma, or a solution comprising hydrogen peroxide such as 5:1H₂SO₄:H₂O₂ at a temperature of 95° C.) for up to about 10 minutes. Anyoxide film (e.g. a native oxide film of silicon dioxide) on the surfacesof the blade 10 to be coated with tungsten is then removed by exposingthe surfaces to a dilute HF solution for up to about 10 minutes.Immediately after the oxide cleaning step, the cutting blade 10 can beloaded into a vacuum chamber (e.g. an evacuated sample chamber of anLPCVD system) wherein a subsequent in situ NF₃ cleaning step isperformed to remove any residual native oxide film. This NF₃ cleaningstep can be performed by heating the blade 10 to about 450° C. andexposing the silicon surfaces to be coated with tungsten to gaseous NF₃for up to 10 minutes. Deposition of the tungsten coating 24 can thentake place in the same LPCVD system at the same elevated temperature byexposing the silicon surfaces to gaseous WF₆ at an overall pressure ofabout 400 milliTorr, for a time period of up to several minutes. The WF₆reacts with any exposed silicon surfaces on the blade 10 to producemetallic tungsten (W) which is conformally deposited over the exposedsilicon surfaces. The deposition of the tungsten coating 24 isself-limiting in that the deposition ceases once all the exposed siliconsurfaces of the cutting blade 10 have been coated with metallic tungstento a thickness of about 5-50 nanometers, since the silicon surfaces arecoated and therefore are no longer accessible to the WF₆.

[0045] In other cases for reasons of biocompatibility or reducedfriction, a conformal coating 24 of parylene can be formed over at leasta portion of the cutting blade 10. This can be done either before orafter attachment of the blade 10 to a handle 26, with the handle 26 inthe latter case also being coated with parylene to form an integralcoated assembly.

[0046] Parylene is a transparent conformal biocompatible coating thatcan be produced by the condensation and polymerization of a gaseousmonomer, para-xylylene, at room temperature using vapor depositionpolymerization (VDP) in a vacuum chamber. Parylene is available in threedimer forms designated as Parylene N (also termed di-para-xylylene orDPX-N), Parylene C (also termed dichloro-di-para-xylylene or DPX-C) andParylene D (also termed tetra-chloro-di-para-xylylene or DPX-D).Parylene can be vapor deposited over the cutting blade 10 to form acoating 24 having a thickness in the range of 0.1 to 10 μm or more.Furthermore, the parylene coating 24 can act as a dry-film lubricant toreduce friction and improve wear resistance of the cutting edge of theblade 10.

[0047] The VDP process takes place in a vacuum environment of 20-70milliTorr and will be described hereinafter with reference to theformation of a Parylene N coating 24. A similar process is used to coatthe cutting blade 10 with Parylene C or Parylene D; and this can be donewith a commercially-available parylene deposition system.

[0048] Using the Gorham process as disclosed in U.S. Pat. No. 3,342,754,which is incorporated herein by reference, a parylene dimer,di-para-xylylene, is heated to about 150° C. resulting in its conversionto a gaseous dimer. This causes the gas pressure in the vaporizationzone to rise, forcing the dimeric gas downstream into a pyrolysis zonewhere it is then heated to about 650° C., splitting the dimer moleculesinto highly reactive monomer molecules of para-xylylene. The monomermolecules continue to respond to pressure, flowing into the depositionchamber where they disperse and grow as a clear linear-polymer film onall surfaces to which the gas is exposed. The thickness of the resultantParylene N coating 24 is controlled by the volume of the parylene dimerthat is vaporized and by the dwell time in the deposition chamber. Sincethe parylene deposition process is gaseous, the coating thickness isuniform and conformal without any associated cure stress. The use ofparylene coatings on surgical instruments is disclosed, for example, inU.S. Pat. No. 5,380,320 which is incorporated herein by reference.

[0049] In depositing the various coatings 24 described above maskingtechniques as known to the semiconductor processing art can be used toprevent the deposition of the coating 24 on particular surfaces of thecutting blade 10 (e.g. on a portion of surface 14 wherein the handle 26is to be attached as shown in FIG. 1A), or to aid in removing thecoating from particular surfaces after deposition.

[0050] FIGS. 3A-3E show a process for fabricating a second example ofthe cutting blade 10 of the present invention in the form of adouble-edged blade 10. Fabrication of the double-edged cutting blade 10is similar to that described previously with reference to FIGS. 2A-2Eexcept that openings 20 are formed in the etch mask 18 on both surfaces14 and 14′ of the {211}-oriented monocrystalline silicon substrate 12,with the openings 20 being laterally offset with respect to each otherand located wherein each cutting edge 16 of the blade 10 is to beformed. The exact locations and shapes of the openings 20 will dependupon a predetermined dimensions for the cutting blade 10 and on how manyedges of the blade 10 are to be formed by etching (e.g. whether just thetwo cutting edges 16 are to be formed by etching or whether theremaining sides of the blade 10 are also to be formed by etching).

[0051] In FIG. 3A, the etch mask 18 is formed over the major bodysurfaces 14 and 14′ as described with reference to FIG. 2A. Elongate(e.g. rectangular or U-shaped) openings 20 are then formed through theetch mask 18 at the location of each cutting edge 16 to be formed.

[0052] In FIG. 3B, both major body surfaces 14 and 14′ of the substrate12 are anisotropically etched through the openings 20 to form the twocutting edges 16. The etching step can proceed as described previouslywith reference to FIG. 2B. As the etching takes place simultaneously onboth surfaces 14 and 14′ of the substrate 12, the cutting edges 16 areformed when the an isotropic wet etching process substantiallyterminates upon reaching a pair of parallel {111} crystalline planes ofsilicon. This results in each cutting edge 16 being oriented at the sameangle θ=19.5° with respect to one of the {211})-oriented major bodysurfaces 14 or 14′ as shown in FIG. 3B. As a result of the etching, theoriginal substrate in FIG. 3A is divided into three portions, with afirst substrate portion that forms the cutting blade 10 being designatedas substrate portion 12 in FIG. 3B, and with the remainder of theoriginal substrate of FIG. 3A being designated as substrate portions 12′and 12″ in FIG. 3B. The substrate portions 12′ and 12″ can be discardedonce fabrication of the blade 10 is completed.

[0053] In FIG. 3C, the etch mask 18 is removed from the substrate asdescribed previously with reference to FIG. 2C. This leaves thesubstrate portions 12, 12′ and 12″ connected together at locationsoutside the elongate openings 20 when the openings 20 in the etch mask18 are rectangular. If each opening 20 were U-shaped (e.g. with a forkedside of one U-shaped opening 20 being oriented to face the forked sideof the other U-shaped opening 20) to allow the remaining sides of thecutting blade 10 to be etched at the same time the cutting edges 16 areformed, then the individual blade(s) 10 can be released from theoriginal substrate upon completion of the etching step since thesubstrate portions 12′ and 12″ would no longer be connected to thesubstrate portion 12 forming the completed blade 10.

[0054] In FIG. 3D, if necessary the substrate portions 12′ and 12″ canbe removed using a conventional dicing technique as described previouslywith reference to FIG. 2D. The resultant double-edged cutting blade 10can then be mounted onto an appropriate handle 26 for use as describedwith reference to FIG. 1A. The various dimensions for the double-edgedcutting blade 10 can be, for example, in the same range as thedimensions previously recited for the single-edged cutting blade 10 ofFIGS. 1A and 1B, with the exact dimensions depending upon a particularuse for the double-edged cutting blade 10.

[0055] In FIG. 3E, the double-edged cutting blade 10 can be optionallycoated as described previously with reference to FIG. 2E, with thecoating 24 comprising, for example, silicon nitride, titanium nitride,tungsten, amorphous diamond or parylene. The coating 24 can cover all ofthe blade 10 as shown in FIG. 3E; or alternately the coating 24 cancover only a part of the blade 10 (e.g. the cutting edges 16 and/or theone or more of the edge-adjoining surfaces 14 and 14′). The coating 24can be formed either before or after removal of the cutting blade 10from the substrate portions 12′ and 12″. In some instances (e.g. forparylene), the coating 24 can be applied after mounting the blade 10 toa handle 26 with the coating 24 covering both the blade 10 and handle26.

[0056] The matter set forth in the foregoing description andaccompanying drawings is offered by way of illustration only and not asa limitation. Other applications and variations of the apparatus andmethod of the present invention will become evident to those skilled inthe art. Those skilled in the art will understand that other shapes forthe opening(s) 20 in the etch mask 18 are possible so that a pluralityof sides of the cutting blade 10 can be simultaneously etched toterminate upon reaching {111} crystalline planes of silicon, with theindividual {111} planes being oriented as described previously withreference to FIGS. 1A and 2B. Furthermore, those skilled in the art willunderstand that other shapes can be used for the handle 26 than thatshown schematically in FIG. 1A, with the shape of a particular handle 26being selected for a particular application of the cutting blade 10.Finally, those skilled in the art will understand that the cutting blade10 of the present invention has uses other than for surgery. Forexample, the cutting blade 10 can be used for shaving, or in amicrotome. The actual scope of the invention is intended to be definedin the following claims when viewed in their proper perspective based onthe prior art.

What is claimed is:
 1. A micromachined cutting blade, comprising: (a) anelongate body of monocrystalline silicon having a pair of substantiallyparallel major body surfaces, with each major body surface being alignedsubstantially coplanar with a {211} crystalline plane of silicon; and(b) a substantially planar cutting edge formed in the monocrystallinesilicon body at an angle to one of the major body surfaces and orientedalong the length of the body.
 2. The blade of claim 1 wherein the angleis 19.5 degrees.
 3. The blade of claim 1 wherein the substantiallyplanar cutting edge is aligned along a {111} crystalline plane ofsilicon.
 4. The blade of claim 1 further including a coating of a hardmaterial covering at least a part of the cutting edge.
 5. The blade ofclaim 4 wherein the coating comprises silicon nitride.
 6. The blade ofclaim 4 wherein the coating comprises titanium nitride.
 7. The blade ofclaim 4 wherein the coating comprises tungsten.
 8. The blade of claim 4wherein the coating comprises amorphous diamond.
 9. The blade of claim 1further including a conformal coating of parylene covering at least aportion of the cutting blade.
 10. The blade of claim 1 further includinga handle connected to opposite ends of the elongate body to support theelongate body in tension.
 11. The blade of claim 10 wherein the handleis U-shaped.
 12. A micromachined cutting blade, comprising: (a) anelongate body of monocrystalline silicon having a pair of substantiallyparallel major body surfaces; and (b) at least one cutting edge formedin the monocrystalline silicon body, with each cutting edge furthercomprising a pair of cutting-edge surfaces aligned along crystallineplanes of silicon and intersecting at an angle of less than 30 degrees.13. The blade of claim 12 wherein the cutting-edge surfaces intersect atan angle of less than 20 degrees.
 14. The blade of claim 13 wherein oneof the cutting-edge surfaces is aligned substantially coplanar with oneof the body surfaces.
 15. The blade of claim 12 wherein the bodysurfaces are substantially coplanar with a {211} crystalline plane ofsilicon.
 16. The blade of claim 15 wherein one of the cutting-edgesurfaces is aligned along the {211} crystalline plane of silicon, andthe other cutting-edge surface is aligned along the {111} crystallineplane of silicon.
 17. The blade of claim 12 further including a coatingof a hard material covering at least a part of one cutting edge.
 18. Theblade of claim 17 wherein the coating comprises silicon nitride.
 19. Theblade of claim 17 wherein the coating comprises titanium nitride. 20.The blade of claim 17 wherein the coating comprises tungsten.
 21. Theblade of claim 17 wherein the coating comprises diamond.
 22. The bladeof claim 12 further including a conformal coating of parylene coveringat least a portion of the cutting blade.
 23. A method for forming amicromachined cutting blade, comprising steps for: (a) providing amonocrystalline silicon body having a pair of substantially parallelmajor body surfaces, with each major body surface being alignedsubstantially along a {211} crystalline plane of silicon; and (b)forming at least one cutting edge in the monocrystalline silicon bodyby: (i) forming an etch mask over each body surface, with the etch maskformed over at least one of the body surfaces having an elongate openingtherethrough to expose a portion of the body surface wherein the cuttingedge is to be formed; (ii) anisotropic etching the exposed portion ofthe body surface through each opening in the etch mask down to theopposite body surface; and (iii) removing each etch mask.
 24. The methodof claim 23 wherein each cutting edge is aligned substantially along a{111} crystalline plane of silicon.
 25. The method of claim 23 furtherincluding a step for hardening each cutting edge by depositing a coatingof a hard material over at least a part of the cutting edge.
 26. Themethod of claim 25 wherein the hardening step comprises depositing thecoating by a vapor deposition process.
 27. The method of claim 26wherein the deposited coating comprises silicon nitride.
 28. The methodof claim 26 wherein the deposited coating comprises titanium nitride.29. The method of claim 26 wherein the deposited coating comprisestungsten.
 30. The method of claim 26 wherein the deposited coatingcomprises amorphous diamond.
 31. The method of claim 23 furtherincluding a step for depositing a conformal coating of parylene over atleast a portion of each cutting blade.
 32. The method of claim 23wherein the step for anisotropic etching the body surface comprisesetching with an anisotropic wet etchant selected from the groupconsisting of potassium hydroxide, tetramethyl ammonium hydroxide andethylenediamine pyrocatechol.
 33. The method of claim 23 furtherincluding a step for attaching a handle to the monocrystalline siliconbody to hold the monocrystalline silicon body and each cutting edge intension.
 34. The method of claim 33 wherein the handle is U-shaped.